<!DOCTYPE html>
<html style="height:100%">

	<head>
		<meta charset=utf-8>
		<title>div高度</title>
		<style>
			/** {
				margin: 0;
				padding: 0
			}*/
			
			.nav {
				width: 30%;
				height: 40%;
				background-color: red;
			}
			.nav1 {
				width: 40%;
				height: 40%;
				background-color: gray;
			}
			.nav2 {
				width: 30%;
				height: 40%;
				background-color: green;
			}
		</style>
	</head>

	<body style="height:100%">
		<div class="nav" style="float:left;">
			divdivdiv
		</div>
		<div class="nav1" style="float:left;">
			divdivdiv
		</div>
		<div class="nav2" style="float:left;">
			divdivdiv
		</div>
	</body>

</html>